One method to control intake and exhaust valve operation during engine operation is described in French Patent application. No. FR2851367 A1. This method presents a means to control electromagnetically actuated valves that may reduce valve noise. The approach attempts to maintain a valve actuator armature plate at a distance between a coil magnetic pole face and the armature/valve neutral position (sometimes referred to as “levitation”) and thereby reduce valve noise since impacts between the valve armature and the coil magnetic pole face. The approach also mentions keeping a small clearance (gap) between the valve actuator armature and a valve stem, which may further reduce valvetrain noise since the armature has less time to accelerate before impacting the valve stem during a valve opening operation.
The above-mentioned method also can have the disadvantage of increasing valve power consumption over an engine cycle. Levitation can increase power consumption because the force produced by an electromagnetic coil acting on an actuator armature decreases as the distance of the armature increases from the coil. Consequently, additional current may be required to position an armature at location that is distant from a magnetic coil pole face. During engine operating conditions where engine speed and operator demand are low, valves in a cylinder are held closed for a large portion of a cylinder cycle (i.e., the crankshaft angle over which operations are performed that produce and outcome, four cylinder strokes in a four cycle engine for example). Therefore, when a valve is closed and when a valve actuator armature plate is maintained at a distance from a coil magnetic pole face, power consumption can increase over a large portion of a cylinder cycle.
The inventors herein have recognized the above-mentioned disadvantage and have developed a method of electromechanical valve control that offers substantial improvements.